Prevent several registration of the same config pojo

This commit detects case where the same set of keys are exposed several
times and prevents the compilation to complete. Previously, duplicate
keys were silently added to the meta-data.

Closes gh-5939

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessor.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -172,11 +172,17 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 			Element returns = this.processingEnv.getTypeUtils()
 					.asElement(element.getReturnType());
 			if (returns instanceof TypeElement) {
-				this.metadataCollector.add(
-						ItemMetadata.newGroup(prefix, this.typeUtils.getType(returns),
-								this.typeUtils.getType(element.getEnclosingElement()),
-								element.toString()));
-				processTypeElement(prefix, (TypeElement) returns);
+				ItemMetadata group = ItemMetadata.newGroup(prefix, this.typeUtils.getType(returns),
+						this.typeUtils.getType(element.getEnclosingElement()),
+						element.toString());
+				if (this.metadataCollector.hasSimilarGroup(group)) {
+					this.processingEnv.getMessager().printMessage(Kind.ERROR,
+							"Duplicate `@ConfigurationProperties` definition for prefix '" + prefix + "'", element);
+				}
+				else {
+					this.metadataCollector.add(group);
+					processTypeElement(prefix, (TypeElement) returns);
+				}
 			}
 		}
 	}

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/MetadataCollector.java

 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -77,6 +77,20 @@ public class MetadataCollector {
 		this.metadataItems.add(metadata);
 	}
 
+	public boolean hasSimilarGroup(ItemMetadata metadata) {
+		if (!metadata.isOfItemType(ItemMetadata.ItemType.GROUP)) {
+			throw new IllegalStateException("item " + metadata + " must be a group");
+		}
+		for (ItemMetadata existing : this.metadataItems) {
+			if (existing.isOfItemType(ItemMetadata.ItemType.GROUP)
+					&& existing.getName().equals(metadata.getName())
+					&& existing.getType().equals(metadata.getType())) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	public ConfigurationMetadata getMetadata() {
 		ConfigurationMetadata metadata = new ConfigurationMetadata();
 		for (ItemMetadata item : this.metadataItems) {

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessorTests.java

@@ -56,11 +56,13 @@ import org.springframework.boot.configurationsample.simple.SimpleTypeProperties;
 import org.springframework.boot.configurationsample.specific.BoxingPojo;
 import org.springframework.boot.configurationsample.specific.BuilderPojo;
 import org.springframework.boot.configurationsample.specific.DeprecatedUnrelatedMethodPojo;
+import org.springframework.boot.configurationsample.specific.DoubleRegistrationProperties;
 import org.springframework.boot.configurationsample.specific.ExcludedTypesPojo;
 import org.springframework.boot.configurationsample.specific.InnerClassAnnotatedGetterConfig;
 import org.springframework.boot.configurationsample.specific.InnerClassProperties;
 import org.springframework.boot.configurationsample.specific.InnerClassRootConfig;
 import org.springframework.boot.configurationsample.specific.InvalidAccessorProperties;
+import org.springframework.boot.configurationsample.specific.InvalidDoubleRegistrationProperties;
 import org.springframework.boot.configurationsample.specific.SimplePojo;
 import org.springframework.util.FileCopyUtils;
 
@@ -342,6 +344,23 @@ public class ConfigurationMetadataAnnotationProcessorTests {
 		assertThat(metadata.getItems()).hasSize(1);
 	}
 
+	@Test
+	public void doubleRegistration() throws IOException {
+		ConfigurationMetadata metadata = compile(DoubleRegistrationProperties.class);
+		assertThat(metadata).has(Metadata.withGroup("one"));
+		assertThat(metadata).has(Metadata.withGroup("two"));
+		assertThat(metadata).has(Metadata.withProperty("one.value"));
+		assertThat(metadata).has(Metadata.withProperty("two.value"));
+		assertThat(metadata.getItems()).hasSize(4);
+	}
+
+	@Test
+	public void invalidDoubleRegistration() throws IOException {
+		this.thrown.expect(IllegalStateException.class);
+		this.thrown.expectMessage("Compilation failed");
+		compile(InvalidDoubleRegistrationProperties.class);
+	}
+
 	@Test
 	public void lombokDataProperties() throws Exception {
 		ConfigurationMetadata metadata = compile(LombokSimpleDataProperties.class);

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/specific/DoubleRegistrationProperties.java

+/*
+ * Copyright 2012-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationsample.specific;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+/**
+ * Test that the same type can be registered several times if the prefix is
+ * different.
+ *
+ * @author Stephane Nicoll
+ */
+public class DoubleRegistrationProperties {
+
+	@ConfigurationProperties("one")
+	public SimplePojo one() {
+		return new SimplePojo();
+	}
+
+	@ConfigurationProperties("two")
+	public SimplePojo two() {
+		return new SimplePojo();
+	}
+
+}

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/specific/InvalidDoubleRegistrationProperties.java

+/*
+ * Copyright 2012-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.configurationsample.specific;
+
+import org.springframework.boot.configurationsample.ConfigurationProperties;
+
+/**
+ * Test that compilation fails if the same type is registered twice with the
+ * same prefix.
+ *
+ * @author Stephane Nicoll
+ */
+public class InvalidDoubleRegistrationProperties {
+
+	@ConfigurationProperties("foo")
+	public Foo foo() {
+		return new Foo();
+	}
+
+	@ConfigurationProperties("foo")
+	public static class Foo {
+
+		private String name;
+
+		public String getName() {
+			return this.name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+
+}